This invention relates to a monolithic ceramic capacitor with lead wires extending therefrom and more particularly to such a capacitor having a solid free-flowed protective coating about the body.
A capacitor of this class having lead wires that are mutually parallel is disclosed in the patent to Coleman, U.S. Pat. No. 3,890,546 issued June 17, 1975. Another capacitor of this class is disclosed in the patent to J. Heron, U.S. Pat. No. 3,710,210 issued Jan. 9, 1973 wherein the leads extend in opposite directions away from the capacitor body. Both of these patents are assigned to the same assignee as is the instant invention.
The lead wires in the above-noted patents each have an enlarged nail-head portion at one end thereof. These leads are each attached by a solder layer between a metal termination region on the body and the end surface of the nail-head. An insulative coating may be applied over the body in liquid form and over the nail-head portions to enhance their strength of attachment.
Although the application of a conformal free-flowed coating in liquid form is substantially less costly than the more disciplined steps of molding or casting, the latter are often chosen for the following reasons.
Conformal free-flowed coatings are typically applied by dipping in liquid resin, shielding and spraying, immersing in a fluidized bed of resin particles or brushing. It is difficult to precisely control the application to a predetermined point along the lead wires. Even when the application is painstakingly controlled, the liquid coating tends to wick further out along the lead wires. These problems are particularly noticeable in tiny monolithic ceramic capacitors for printed wire board mounting wherein the lead wires are relatively large compared with the capacitor body that must be coated, since a unit variation in any dimension of the coated portion of the capacitor tends to be a larger percentage of a smaller component, and the lead diameter not being reduced proportionally provides nearly the same expanse of wicking surface as for the larger component.
It is therefore an object of the present invention to provide a low cost free-flow coated monolithic ceramic capacitor having lead wires butt-attached thereto.
It is a further object of this invention to provide such a capacitor capable of being manufactured with relatively uniform physical dimensions.
It is yet a further object of this invention to provide such a capacitor capable of being manufactured without the aforementioned liquid coating wicking problems.